We plan a Program Project to develop and assess a general model of normal and disordered cognition. The model is intended to bridge the gap between the growing understanding of the biological disorders that can affect cognition and the growing body of behavioral evidence on the precise nature of the resulting deficits. The model embodies a set of principles that provide a starting place for capturing basic aspects of normal cognition and effects of brain damage, developmental anomalies, and disorders of neuromodulation on cognitive processes. We present three part-projects designed to investigate the adequacy of the model, using computer simulation of behavioral data to be obtained from normal, schizophrenic, and brain-damaged populations. Part 1 outlines work designed to establish whether several general laws of information processing can be accounted for as emergent properties of processing systems that adhere to the principles of the model, and applies the model to two well studied information processing tasks involving the use of context and attention to control processing. Part 2 explores the effects of disorders of neuromodulation on information processing. It uses the model to examine how well behavioral deficits seen in schizophrenic patients can be accounted for by assuming a reduction in the responsivity of dopamine-sensitive neurons in prefrontal cortex. Part 3 examines one specific type of acquired information processing skill (word identification and naming), and seeks to establish a model that accounts for normal skilled performance, the development of processing ability, the effects of brain damage, and developmental anomalies. The Core component of the project will provide mechanisms to facilitate further development of the model and the incorporation of neurobiological evidence, as well as the computational resources needed to assess the adequacy of the model. The project would contribute directly to our understanding of the processes underlying normal cognition and of the precise understanding of the disorders that arise from damage or disturbance of the underlying biological processes.